Conductive fluid logging sensor and method

ABSTRACT

In a borehole logging tool, the flow of conductive fluid into or out of a wellbore at the wellbore wall is detected and measured with a sensor loop proximate the borehole inner wall. The sensor loop includes a series of contiguous sensors that act as electromagnetic flowmeters and provide fluid measurements covering the entire circumference of the sensor loop. The sensor loop includes an elastic element that forces the sensor loop outward to maintain pressure along the sensor loop circumference against the interior borehole wall. The sensor loop is designed to lie at a non-perpendicular angle to the wellbore axis, and mechanical arms press the top and bottom of the loop against the borehole inner wall.

TECHNICAL FIELD

[0001] This invention relates generally to oil and gas well productionlogging sensors and methods, and more particularly to a sensing deviceand method for detecting fluid influx into a well.

BACKGROUND

[0002] An oil and gas well is shown in FIG. 1 generally at 60. Wellconstruction involves drilling a hole or borehole 62 in the surface 64of land or ocean floor. The borehole 62 may be several thousand feetdeep, and drilling is continued until the desired depth is reached.Fluids such as oil, gas and water reside in porous rock formations 68. Acasing 72 is normally lowered into the borehole 62. The region betweenthe casing 72 and rock formation 68 is filled with cement 70 to providea hydraulic seal. Usually, tubing 74 is inserted into the hole 62, thetubing 74 including a packer 76 which comprises a seal. A packer fluid78 is disposed between the casing 72 and tubing 74 annular region.Perforations 80 may be located in the casing 72 and cement 70, into therock 68, as shown.

[0003] Production logging involves obtaining logging information aboutan active oil, gas or water-injection well while the well is flowing. Alogging tool instrument package comprising sensors is lowered into awell, the well is flowed and measurements are taken. Production loggingis generally considered the best method of determining actual downholeflow. A well log, a collection of data from measurements made in a well,is generated and is usually presented in a long strip chart paper formatthat may be in a format specified by the American Petroleum Institute(API), for example.

[0004] The general objective of production logging is to provideinformation for the diagnosis of a well. A wide variety of informationis obtainable by production logging, including determining water entrylocation, flow profile, off depth perforations, gas influx locations,oil influx locations, non-performing perforations, thief zone stealingAttorney Docket No. production, casing leaks, crossflow, flow behindcasing, verification of new well flow integrity, and floodwaterbreakthrough, as examples. The benefits of production logging includeincreased hydrocarbon production, decreased water production, detectionof mechanical problems and well damage, identification of unproductiveintervals for remedial action, testing reservoir models, evaluation ofdrilling or completion effectiveness, monitoring Enhanced Oil Recovery(EOR) process, and increased profits, for example. An expert generallyperforms interpretation of the logging results.

[0005] In current practice, measurements are typically made in thecentral portion of the wellbore cross-section, such as of spinnerrotation rate, fluid density and dielectric constant of the fluidmixture. These data may be interpreted in an attempt to determine theflow rate at any point along the borehole. Influx or exit rate over anyinterval is then determined by subtracting the flow rates at the twoends of the interval.

[0006] In most producing oil and gas wells, the wellbore itselfgenerally contains a large volume percentage or fraction of water, butoften little of this water flows to the surface. The water that doesflow to the surface enters the wellbore, which usually already containsa large amount of water. The presence of water already in the wellbore,however, makes detection of the additional water entering the wellboredifficult and often beyond the ability of conventional productionlogging tools.

[0007] Furthermore, in deviated and horizontal wells with multiphaseflow, and also in some vertical wells, conventional production loggingmethods are frequently misleading due to complex and varying flowregimes or patterns that cause misleading and non-representativereadings. Generally, prior art production logging is performed in thesecomplex flow regimes in the central area of the borehole and yieldsfrequently misleading results, or may possess other severe limitations.Often the location of an influx of water, which is usually theinformation desired from production logging, is not discernable due tothe small change in current measurement responses superimposed uponlarge variations caused by the multiphase flow conditions.

[0008] The problems of production logging in multi-phase flow inconventional production logging are well known and described in theliterature. Hill, A. D., et al., in an article entitled, “ProductionLogging Tool Behavior in Two-Phase Inclined Flow”, JPT, October 1982,pp. 2432-2440, describe the problems of conventional production loggingin multiphase wells, stating that for production logging purposes, awell is deviated if it has a deviation over two degrees. Virtually allproducing wells have deviations of at least two degrees, and thusvirtually all wells are subject to difficult multiphase flow conditionsfor production logging. Hill et al. also describe the four main types ofmeasurements in use in conventional production logging practice, whichare the spinner, dielectric constant, fluid density, and concentratingflowmeter.

[0009] A more extensive description of conventional production loggingmeasurements and the problems encountered in multiphase flow is found ina monograph entitled “Production Logging—Theoretical and InterpretativeElements”, by Hill, A. D., Society of Petroleum Engineers, MonographVolume 14, Richardson, Texas, 1990. In addition, the followingpublications discuss the problems of measuring multiphase flow indeviated or horizontal wells: “Tests Show Production Logging Problems inHorizontal Gas Wells” by Branagan, P., et al., Oil & Gas Journal, Jan.10, 1994, pp. 41-45; “Biphasic Fluid Studies for Production Logging inLarge-Diameter Deviated Wells” by Kelman, J. S., November-December 1993,The Log Analyst, pp. 6-10; “A Comparison of Predictive Oil/Water HoldupModels for Production Log Interpretation in Vertical and DeviatedWellbores” by Ding, Z. X., et al, SPWLA 35th Annual Logging SymposiumTransactions, June 1994, paper KK; and “Production Logging in HorizontalWellbores” by Nice, S. B., 5th World Oil. Horizontal Well Technol. Int.Conf. (Houston) Proc., sect. 11, November 1993.

[0010] While very few wells are actually vertical, the followingpublication illustrates that conventional production logging may bemisleading even in truly vertical wells: “The Effect of Flow FromPerforations on Two-Phase Flow: Implications for Production Logging” byZhu, D., et al., Proceedings SPE Annual Technical Conference andExhibition, SPE 18207, October 1988, p. 267-75.

[0011] U.S. Pat. No. 5,551,287 entitled, “Method of Monitoring FluidsEntering a Wellbore”, issued Sep. 3, 1996 to Maute et al. addresses theabove problems. However, the invention has limitations in that it ismechanically complex, and is sensitive in different ways to all threefluids encountered downhole (water, gas, and oil), which results incomplex log interpretation, and possibly misleading log interpretation.For example, the interpretation may be misleading if gas does not coolupon entry to the wellbore, as it usually but not always does. Theinterpretation is also complicated when the wellbore contains asignificant amount of non-produced water as is generally the case,making the distinguishing of inflow of water from non-produced waterdifficult and ambiguous. In addition, the tool is designed for only onecasing diameter, and cannot readily accommodate any significantlydifferent diameter, as does occur in many wells. Furthermore, a largeamount of data is needed from each of the multitude of pads (eight ormore), each of which has three different sensors.

SUMMARY OF THE INVENTION

[0012] The present invention provides an apparatus for and a method ofmeasuring the flow of fluid as it enters or exits a wellbore before itbecomes substantially intermixed with the fluids and the often complexflow pattern already in the wellbore.

[0013] In accordance with a preferred embodiment, a logging deviceutilizes a sensor loop comprising a plurality of electrodes to sense theflow of water in a wellbore. The sensor loop may include a spring forexerting continuous pressure against the wellbore wall and includes atleast one current coil adapted to generate a magnetic field. Bymeasuring the voltage induced by the magnetic field and conductive fluid(e.g., water) movement within the wellbore perpendicular to the magneticfield, the lateral flow rate of the water can be determined. The loggingdevice may include at least two arms adapted to maintain the sensor loopforce against the wellbore wall while moving up and down within thewellbore, even with varying borehole diameters.

[0014] Disclosed is a preferred embodiment of a logging tool for aborehole, the borehole having an interior wall, the tool comprising atool body adapted to be inserted into the borehole, and a radial sensingdevice coupled to the tool body, the radial sensing device adapted tomeasure the flow velocity of conductive fluid entering or leaving theborehole interior wall, the radial sensing device being adapted to makethe conductive fluid flow velocity measurements proximate the boreholewall.

[0015] Also disclosed is a preferred embodiment of a fluid flowmeasuring device, comprising a plurality of resistors disposed in a looppattern, a plurality of electrodes, each electrode coupled between twoadjacent resistors, a first coil of wire adapted to generate a magneticfield wound proximate the resistors and electrodes, a second coil ofwire adapted to generate a magnetic field wound proximate the resistorsand electrodes, and a voltage measuring mechanism electrically coupledbetween two of the resistors, wherein a flow of conductive fluid isdetectable by measuring the voltage.

[0016] Further disclosed is a preferred embodiment of a method ofmeasuring lateral fluid flow into a borehole, comprising traversing theborehole with a tool body having a sensor loop attached thereto, whereinthe sensor loop is adapted to directly measure the flow velocity ofconductive fluid entering or leaving the borehole interior wall.

[0017] Advantages of preferred embodiments of the invention includeproviding a logging device that is sensitive only to conductive fluidssuch as water, and not sensitive to non-conductive fluids such as oil orgas. Only water entering or exiting the wellbore is sensed as it entersor exits, and the sensor loop is not sensitive to water already in theborehole, whether the water is moving or not. The device is notsensitive to the complex flow regimes in the center of the wellbore,because preferred embodiments of the invention measure the flow as itenters the wellbore along the wall and before it enters into the complexflow regimes in the wellbore center. Inferring the cause of changes inabove and below readings is not required as in the prior art; rather,the novel logging device directly senses water entering or leaving thewellbore. Also, the device is not required to infer the type of fluidentering the borehole, as preferred embodiments of the invention aresensitive only to conductive fluids. The measurement sensor loop has nomoving parts, as in some prior art logging instruments that comprisespinners, for example. The sensor loop has no threshold fluid velocitybelow which the measurement registers no flow; thus the sensor loop willsense even a small fluid flow.

[0018] Preferred embodiments of the present invention provide a directmeasurement of the information that must generally be inferred byproduction engineers, that is, where water is entering the borehole.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above features of preferred embodiments of the presentinvention will be more clearly understood from consideration of thefollowing descriptions in connection with accompanying drawings inwhich:

[0020]FIG. 1 shows an oil or gas well;

[0021]FIG. 2 illustrates a cross-sectional view of a wellbore with thesensor loop of a preferred embodiment of the present inventionpositioned within the wellbore;

[0022]FIG. 2A shows a perspective view of the sensor loop movingdownhole towards a water inflow;

[0023]FIG. 2B shows the sensor loop positioned over a water inflow, andthus sensing the water inflow, during its downhole movement;

[0024]FIG. 3 shows a logging tool in a casing of a given inner diameter;

[0025]FIG. 3A shows the logging tool in the same well in a casing withan inner diameter smaller than that of FIG. 3;

[0026]FIG. 4 depicts a side view of a side arm against the casing wallwith the upper part of the sensor loop passing through a recess in theside arm;

[0027]FIG. 4A shows a view of the same items of FIG. 3 from outside thecasing looking radially inward;

[0028]FIG. 4B shows a view from the end of the logging tool of part ofthe sensor loop and a mechanism for attaching the sensor loop to theside arm;

[0029]FIG. 4C shows the bottom of the sensor loop and the side arm;

[0030]FIG. 4D shows the bottom of the sensor loop and the side arm witha radial view from outside the casing;

[0031]FIG. 5 shows the fixed ends of the force arms at the tool body;

[0032]FIG. 5A shows the axially moving ends of the force arms at thetool body;

[0033]FIG. 5B shows the slot in the tool body in which the moving endsof the force arms move axially;

[0034]FIG. 5C shows the smooth hinge and junction of the force arms withthe side arms;

[0035]FIG. 5D illustrates a side view of mechanical elements of alogging tool;

[0036]FIG. 6 depicts a side view of the sensor loop riding over aprotrusion from the casing into the wellbore;

[0037]FIG. 7 shows water flow through a magnetic field producing aninduced and measurable voltage;

[0038]FIG. 8 shows a perspective view of the sensor loop and its variouscomponents;

[0039]FIG. 8A shows a perspective view of how the water flow velocitymeasurement is made on one segment of the sensor loop;

[0040]FIG. 9 shows a schematic of the flow-measuring electrical circuitof the sensor loop;

[0041]FIG. 10A illustrates a top view of the sensor loop;

[0042]FIG. 10B shows a cross-sectional view of the sensor loop; and

[0043]FIG. 11 shows an example of a log response chart.

[0044] Corresponding numerals and symbols in the different figures referto corresponding parts unless otherwise indicated. The figures are drawnto clearly illustrate the relevant aspects of the preferred embodiments,and are not necessarily drawn to scale.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0045] There are many disadvantages in prior art methods and tools fordetecting water flow. For example, prior art devices and techniques aresensitive to all fluids, including water, oil and gas, which leads toambiguity in the determination of what fluid is involved. Fluid entry orexit must be inferred from the wellbore from measurements made in thecenter of the borehole in complex and changing flow regimes above andbelow the point of interest, and the assumption that any change is dueto inflow or outflow must be made. Prior art methods do not directlysense water entering or leaving the wellbore, and are sensitive to wateralready in borehole, whether the water is moving or not. Thedetermination of which type of fluid, water, oil or gas, is entering orexiting the borehole must be inferred by looking at changes inmeasurements made above and below the entry or exit and inferring whichtype of fluid made the changes. The measurements are made in the centerof the borehole in complex and changing flow regimes, which results inambiguity of interpretation.

[0046] In prior art designs, the measurement device typically has movingparts, such as a spinner, which is also called the flowmeter. Thesemoving parts may become jammed with debris in the wellbore flow streamand become useless at times. A spinner is sensitive to moving wateralready in borehole, and has a threshold fluid velocity below which thespinner registers no flow, even though a small flow is present. Priorart measurement tools do not directly measure where water is enteringthe borehole.

[0047] Preferred embodiments of the present invention eliminate theseproblems in the prior art by directly measuring water inflow or outflowthrough the borehole or casing wall. Preferred embodiments of thepresent invention may provide the depths and rates of water inflow oroutflow. Almost all inflow or outflow is one phase, and so the flow ismeasured before it can combine into complex flow patterns with otherphases. Preferred embodiments of the present invention are thusinsensitive to the complex multiphase flow patterns found inside thewellbore. Preferred embodiments of the present invention also aresensitive to only lateral water flow into or out of the wellbore, andare not sensitive to water flow up or down inside the wellbore.Preferred embodiments of the invention may also accommodate changes inthe wellbore inner diameter. Preferred embodiments of the invention areinsensitive to the flow of oil or gas, allowing certain determination ofthe inflow or outflow of water, which is usually the information desiredto be obtained from production logging.

[0048] Preferred embodiments of the present invention will next bedescribed with reference to FIGS. 2 through 11. Referring first to FIG.2, a logging tool 140 includes a main tool body 101 and two centralizingside arms 102 and 103. The tool body 101 preferably comprises steel andmay alternatively comprise titanium, as examples. The tool body 101 maybe 8 feet long and 1 inch wide, for example. The side arms 102/103preferably comprise steel and may alternatively comprise titanium, asexamples. The side arms 102/103 may be 5 feet long and ½ inch wide, forexample. The side arms 102 and 103 are forced against the wellbore 111 aor casing 111 b by force arms 104, 105, 106, and 107. Force arms104/105/106/107 preferably comprise spring stainless steel, as anexample. The force arms 104/105/106/107 may be 1 feet long and ⅛ inchwide, for example. The wellbore 111 a is also referred tointerchangeably herein as a borehole. Typically, a wellbore 11 a islined with a casing 111 b for the entire well. Embodiments of thepresent invention may be utilized in either a cased wellbore or in anopenhole wellbore with no casing, for example.

[0049] In accordance with a preferred embodiment of the presentinvention, a radial sensing device 108 preferably comprising a sensorloop may be attached at radial sensing device 108 upper and lower endsto the two side arms 102 and 103. An electrical line or slickline 109may be coupled to the logging tool 140 and may be adapted to transportthe logging tool 140 to and from the surface. The electrical line 109may transmit electrical power down to the logging tool 140 and maytransmit the measured voltage to a voltage measuring and recordingdevice 110 on the land surface. Note that the measuring and recordingdevice 110 may alternatively reside within the logging tool body 101 asa memory device, and the tool 140 may be operated with an internalelectrical power source, such as batteries.

[0050]FIG. 2A illustrates a perspective view of the sensor loop 108positioned against the inside of the casing 111 b wall, the sensor loop108 being adapted to move upward and downward over perforation holes 112through the casing 111 b towards an inflow of water 113 through aperforation hole 112. In an oil or gas well, water inflow isundesirable, therefore the location of the water inflow is importantinformation to obtain so that the casing 111 b can be repaired, forexample. No inflow of water is measured in the sensor loop 108 positionshown in FIG. 2A because there is no inflow of water 113 anywhere overthe sensor loop 108. Preferably, the sensor loop 108 remains flush withthe casing 111 b or wellbore 111 a interior wall, to maintain closeproximity to regions of inflow of water 113, in order to directly sensethe inflow of water 113. FIG. 2B shows the sensor loop 108 against theinside of the casing wall 111 b moving downward and actually at thelocation of the inflow of water 113 through a perforation hole 112. Inthis position the sensor loop 108 detects the inflow of water 113.

[0051] An embodiment of the present logging tool 140 is adapted tomeasure the location and flow rate of a conductive fluid such as waterentering or leaving a wellbore 111 a or other flow conduit, such as awater pipeline or a chemical line or a sewer line. Sensor loop 108 ispreferably mounted on a logging tool body 101 such that the sensor loop108 is forced radially against the inside of the wellbore 111 a orcasing 111 b wall. The sensor loop 108 is designed such that it liesapproximately in a plane, the plane preferably being oriented at anon-perpendicular angle (e.g., ranging from 10 to 80 degrees, and morepreferably, approximately 45 degrees) to the borehole central axis. Wheninserted into a borehole, the loop 108 may not lie completely in a planedue to it being compressed to fit within the borehole.

[0052]FIGS. 3 and 3A depict the present logging tool 140 in use withindifferent diameter casings 111 b, which may be located within the samewell, for example. The sloped force arms 104/105/106/107 allow the tool140 to enter smaller diameter casings 111 b, forcing the side arms102/103 closer to the tool body 101. The tilt or angle of the sensorloop 108 with respect to the borehole central axis changes from onecasing 111 b inner diameter to another, as seen from FIG. 3 to FIG. 3A.The sensor loop 108 preferably is substantially close to lying within asingle plane, but sensor loop 108 may not necessarily always lie exactlyin a plane, depending upon the diameter of the casing 111 b.

[0053] The top 108 a and bottom 108 b of the sensor loop 108 are heldagainst the inner wall of the borehole 111 b. A preferred method ofholding the top 108 a and bottom 108 b of the sensor loop 108 againstthe inner wall or casing 111 b of the borehole is to mount the top 108 aand bottom 108 b of the sensor loop 108 on each of two side arms 102 and103, respectively, as shown in FIGS. 3 and 3A. The side arms 102/103 arepositioned substantially parallel to the main body 101 of the tool 140and are pressed flat against the inner casing 111 b wall. The two sidearms 102/103 are forced against the casing 111 b wall along their entirelength, such as by force arms 104/105/106/107 which act as bow-springcentralizers at the end of each side arm 102/103. The remainder of thesensor loop 108 substantially everywhere on its circumference forcesitself, by virtue of the elasticity of the sensor loop 108, to liesubstantially flush against the inner wall of the casing 111 b.

[0054]FIG. 4 shows a side view of the mounting of the sensor loop 108 ateach of the side arms 102/103 according to an embodiment of the presentinvention. The sensor loop 108 is preferably mounted to the side arm 102in a recess 114 within the side arm 102. The recess 114 preferably hasgently sloping ends at 114 a to allow space for the thickness of thesensor loop 108 within the side arm 102 and to avoid the tool hanging upon any protrusion from the casing. The recess 114 with sloping ends 114a allows the side arm 102 to ride substantially flush to the casinginner wall 11 b. A rolling mechanism 118 which may comprise, forexample, ball rollers or other rolling mechanism, may be used to reducewear on the side arm 102 and friction when the logging tool 140 movesalong the casing inner wall 111 b. Ball rollers 118 preferably comprisesteel and may alternatively comprise titanium, as examples. Ball rollers118 may be ¼ inch in diameter, for example.

[0055] The sensor loop 108 may be mounted to the side arm 102 with analignment pin 116. Alignment pin 116 preferably comprises steel and mayalternatively comprise titanium, as examples. Alignment pin 116 may be ½inch long and ⅛ inch in diameter, for example. Alignment pin 116preferably is coupled to the sensor loop 108 and resides within a slot115 in the side arm 102. Slot 115 may be 4 inches long, for example. Thealignment pin 116 is adapted to maintain the plane of the sensor loop108 relative to the logging tool 140 and is adapted to prevent the planeof the sensor loop 108 from rotating. The slot 115 in the side arm 102preferably has sloped ends, as shown, to allow some tilt by the sensorloop 108 cross-section if needed to free the sensor loop 108 from asnag. A slide ring 117 may be disposed around the side arm 102 coupledto the sensor ring 108 and alignment pin 116, the slide ring 117 beingadapted to maintain the sensor loop 108 substantially against the sidearm 102 within recess side arm 114 but allowing the sensor loop 108 tomove up or down along the side arm 102 within recess 114 as needed whenentering a different inner diameter casing 111 b. Slide ring 117preferably comprises steel and may alternatively comprise titanium, asexamples. Slide ring 117 may be ⅛ inch thick and ⅜ inch in diameter, forexample.

[0056]FIG. 4A shows side arm 102 and the upper end of the sensor loop108 from a view outside the casing 111 b looking radially inward. Theslot 115 in the side arm 102 for the alignment pin may be seen withinside arm recess 114, as well as the roller balls 118 in the side arm102.

[0057]FIG. 4B shows a view of the sensor loop mounting mechanism fromeither end of the side arm 102. The alignment pin 116 coming out of thesensor loop 108 is shown with the slide ring 117. The side arm 102 maybe substantially cylindrical in shape, but may also comprise othershapes.

[0058]FIG. 4C illustrates the mounting of the sensor loop 108 on theside arm 103, similar to FIG. 4, except FIG. 4C shows the other side arm103. Again, the sensor loop 108 is mounted to the side arm in a recess114 within the side arm 103. This mechanism allows the side arm 103 toride substantially flush to the casing 111 b inner wall. Ball rollers118 or an alternative rolling mechanism may be used to reduce wear onthe side arm 103 and friction when the logging tool 140 moves along thecasing 111 b inner wall. The sensor loop 108 is preferably mounted withan alignment pin 116 coupled to the sensor loop 108 and running out thesensor loop 108 and through a slot 115 in the side arm 103. Thealignment pin 116 maintains the plane of the sensor loop relative to thelogging tool and prevents the plane of the sensor loop from rotating.The slot 115 in the side arm 103 preferably has sloped ends as shown toallow some tilt by the sensor loop 108 cross section if needed to freethe sensor loop 108 from a snag. The slide ring 117 maintains the sensorloop 108 substantially against the side arm 103 within recess 114 butallows the sensor loop 108 to move up or down along the side arm 103within recess 114 as needed when entering a different inner diametercasing 111 b. An optional shield 114 a, comprising a fluoropolymerresin, and alternatively comprising nylon, for example, may be coupledto the side arm 103 to cover the recess 114 and prevent the sensor loop108 from snagging on protrusions along the casing 111 b wall.

[0059]FIG. 4D shows side arm 103 and the lower end of the sensor loop108 from a view outside the casing looking radially inward. The slot 115in the side arm 103 for the alignment pin is visible within the recess114. Roller balls 118 in the side arm 103 are also visible.

[0060]FIG. 5 shows the fixed force arms 119 coupled to one end of thetool body 101. Preferably, the force arms 119 at one end of the loggingtool 140 are fixed firmly to the tool body 101 to maintain the two sidearms 102/103 and the tool body 101 in one plane. The force arms 119provide an outward force to force the side arms 102/103 against theinner wall of the casing 111 b. The outward force may be achieved fromthe elasticity of the metal force arms 119, or from spring loading orother mechanisms, for example.

[0061]FIG. 5A illustrates the moving force arms 120 at the opposite endof the logging tool 140 from the fixed force arms 119 at the other endof the tool 140. Force arms 120 also push the side arms 102/103 outwardand against the casing 111 b inner wall. Preferably, by the geometry ofthe tool 140 design, the force arms 120 on at least one end of the tool140 are adapted to move axially, e.g., along the axis of the wellborewithin the borehole 111 a, to allow for entry of the logging tool 140into different inner diameter casings 111 b. The moving force arms 120may be coupled firmly to a thin flat plate or pin 121 a that movesaxially in a slot 121 through the tool body 101, for example (notshown). Alternatively, the force arms 120 may be fixed at both ends,moveable at both ends, or movable at the top and fixed at the bottom.

[0062]FIG. 5B shows a side view of the tool body 101 (oriented 90degrees to the view of FIG. 5A). The slot 121 is shown that the plate orpin 121 a coupled to the moving force arms 120 is adapted to movewithin. Pin 121 a preferably comprises steel and may alternativelycomprise titanium, as examples. Pin 121 a may be ¼ inch long and ⅛ inchin diameter, for example.

[0063]FIG. 5C demonstrates a preferred method of connecting a force armto a sidearm, in this case force arm 104 to side arm 102. Force arm 104is connected to side arm 102 with a smooth hinge 122, such that no lipexists anywhere to hang up the tool 140 when the force arm 104 enters asmaller diameter casing 111 b. Hinge 122 preferably comprises steel andmay alternatively comprise titanium, as examples. Hinge 122 may be ½inch in width and 4 inches in length, for example.

[0064] When the logging tool 140 enters a larger diameter casing 111 b,such as going out of tubing and into larger diameter casing, the forcearms 119 and 120 push the side arms 102/103 radially outward to contactthe larger diameter borehole 111 b. The moving end of the force arms 120slides in its slot 121 towards the fixed end of the force arms 119.Similarly, when the tool 140 enters a smaller diameter portion of thewellbore 111 b, the slope of the force arms 119 or 120 in contact withthe end of the new diameter tubular 111 b causes a radially inward forceon the force arms 119 or 120 which compresses the force arms 119 or 120radially towards the tool body 101. The moving force arms 120 move inslot 121 axially away from the fixed end force arms 119. Once in the newdiameter casing 111 b or borehole 11 a, be it larger or smaller, theside arms 102/103 are forced by the force arms 119/120 to becomesubstantially flush with the new borehole 111 a or 111 b wall.

[0065]FIG. 5D illustrates a cross-sectional view of the logging tool 140with the sensor ring 108 coupled to the side arms by alignment pin 116(not shown) and slide ring 117, within slot 115 in side arms 102/103.Side arms 102/103 are coupled to force arms 119, which force arms 119are fixably coupled to tool body 101. At the other end of the tool 140,side arms 102/103 are coupled to force arms 120, which force arms 120are moveably coupled to tool body 101 within tool body slot 121 byplate/pin 121 a. As the tool 140 is moved to a portion of the borehole111 a having a smaller diameter, dimension x is decreased, whiledimension y increases, and the angle of the sensor loop 108 to thecentral axis of the borehole 111 a is decreased, accordingly.

[0066] Preferably, the force arms 119/120 at either end of the two sidearms 102/103 are tapered towards the main body 101 of the tool 140 toallow the arms 102/103 to move radially in or out, in conformance withany changes in the inner diameter of the wellbore 111 a or casing 111 b.As the side arms move radially in or out to a wall with a differentdiameter, the side arms move the top and bottom of the sensor loop 108in or out, also. The sensor loop 108 forces itself substantiallyeverywhere against the inside of the wall 111 a/11 b with the newdiameter. Thus, preferred embodiments of the present invention 140 mayaccommodate various wall 111 a/111 b diameters within one well.

[0067]FIG. 6 demonstrates that the sensor loop body 136 cross-sectionmay be sloped at an angle with respect to the casing wall 111 b toenable the sensor loop 108 to ride over small protrusions 123 extendingout of the casing wall 111 a. This is advantageous because it willprevent the tool 140 from hanging up during logging.

[0068]FIG. 7 illustrates the water flow measurement physics principleimplemented by the radial sensing device 108 of a preferred embodimentof the present invention, which is based upon Faraday's law of inducedvoltage. A magnetic field 128 substantially perpendicular to a flow 113of water or other conductive liquid generates a voltage difference 133perpendicular to both the magnetic field 128 and the water flowdirection 113. This induced voltage 133 is detectable with a pair ofelectrodes 129 coupled by wires 130 to a measuring device 110 which maycomprise a voltmeter, for example. Preferably an alternating magneticfield 128 is used which results in an alternating measured voltage 133.Using an alternating magnetic field 128 reduces the effects of electrodepolarization and voltages resulting from complex electrochemicalprocesses.

[0069] The electrodes 129 are positioned along the sensor loop 108,acting as sensors, with each pair of sensors comprising a smallelectromagnetic flowmeter. An electromagnetic flowmeter is a flowmeasurement method, the method comprising placing a magnetic field 128at right angles to the flow 113 of a conductive fluid and then measuringthe voltage 133 between the flowmeters. In a preferred embodiment of thepresent invention, the magnetic field 128 is at right angles to a casing111 a/111 b diameter of the sensor loop 108 through the waterinflow/outflow location. Water has the necessary conductivity to bemeasured, but oil and gas do not. Therefore, preferred embodiments ofthe present invention are insensitive to the flow of oil or gas, andsensitive only to the flow of water flowing radially inward or outwardof the wellbore. Preferred embodiments of the present invention are notsensitive to the flow of water inside the wellbore along the axis of theborehole 111 a/111 b, whether that water is moving towards the top orthe bottom of the well. When water flows through the magnetic field 128,a voltage 133 is induced perpendicular to the magnetic field 128 andperpendicular to the diameter along which the water enters the wellbore111 a/111 b. Two electrodes 129 or sensors on either side of the waterflow 113 detect this voltage 133. This induced voltage 133 is directlyproportional to the water fluid 113 velocity, and reverses in sign ifthe water flow is out instead of in.

[0070]FIG. 8 shows a preferred embodiment of the sensor loop 108 adaptedto make a voltage measurement described herein. The sensor loop 108 ispositioned substantially flush to the casing 111 b. The sensor loop 108comprises a sensor loop body 136. The sensor loop body 136 preferablycomprises fluoropolymer resin and may alternatively comprise nylon, asexamples. The sensor loop body 136 may be ¼ inch wide, ⅜ inch long, and24 inches in diameter, for example.

[0071] The sensor loop body 136 preferably encloses two coils of wire125 and 126, the coils 125/126 being adapted to carry current to inducea magnetic field 128. Coils 125/126 preferably comprise a copper alloy,and may alternatively comprise other conductive materials such asaluminum, as examples.

[0072] The magnetic field 128 is generated by a current run through thetwo coils 125/126 of wire in the sensor loop 108, each coil 125/126running around the entire length of the sensor loop. The two coils125/126 carry current in opposite directions so that the magnetic fieldfrom each coil 125/126 is in the same direction between the coils125/126, and tends to cancel inside the inner coil 125 and outside theouter coil 126. A soft ferromagnetic material 127 is preferablypositioned between the coils 125/126, the ferromagnetic material 127adapted to increase the strength of the magnetic field 128 between coils125/126. Ferromagnetic material 127 preferably comprise an iron alloy,and may alternatively comprise other magnetic materials such as nickel,as examples.

[0073] The ferromagnetic material 127 may be ⅛ inch wide, for example.

[0074] Electrodes 129 are coupled along the exterior of the sensor loopbody 136 and are adapted to detect a voltage difference between eachadjacent pair of electrodes 129.

[0075] Electrodes 129 preferably comprise a copper alloy, and mayalternatively comprise other conductive materials such as aluminum, asexamples. Electrodes 129 may be ⅛ inch wide and ⅛ inch long, forexample.

[0076] The sensor loop 108 is spring-loaded, which feature isaccomplished by the sensor loop 108 comprising a spring or force loop124 being adapted to exert outward pressure to maintain contact of thesensor loop 108 substantially flush with the borehole interior wallwhile the tool traverses the borehole. Force loop 124 preferablycomprises an elastic material, such as stainless steel spring wire, andmay alternatively comprise bronze. The force loop 124 is preferablyimbedded in the sensor loop body 136 to provide a mechanical force topress the sensor loop 108 substantially everywhere against the insidewall of the wellbore 111 a or casing 111 b regardless of the bore orcasing interior diameter.

[0077] The electrodes 129 are preferably spaced equidistant from oneanother, at regular spacings, with each spacing distance preferablybeing somewhat about or less than the diameter of a perforation hole 112(shown in FIG. 8A). Electrodes 129 are contiguous to each other and ringthe entire sensor loop 108 to cover the full circumference of the sensorloop 108 and thus the full interior of the casing 111 b wall.

[0078] One electrode 129 can act as the right electrode for a pair ofelectrodes and also simultaneously act as the left electrode for thenext adjacent pair, so that a series of substantially equally spacedelectrodes 129 exists at the surface of the sensor loop 108.

[0079] These electrodes 129 are preferably coupled in series to eachother with a high value resistor (shown in FIG. 9) between each. If thetotal voltage between one pair of electrodes 129 without an interveningresistor 132 is measured and recorded (e.g., by voltage meter 110, shownin FIG. 9), this voltage 133 is indicative of the fluid flow 113 rate(shown in FIG. 8a). Preferably the pair of electrodes 129 without anintervening resistor 132 are in close proximity to one another tominimize the amount of insensitive measuring length between them.

[0080] The measured voltage 133 is proportional to the equivalent flowvelocity through one perforation hole 112 (shown in FIG. 8a). If theperforation hole 112 diameter is known (from known information about thetype of charge that made it) or estimated (typically 0.3 inches indiameter, for example), the inflow or outflow rate at that depth withinthe well may also be determined.

[0081] In a preferred embodiment, the magnetic field 128 is alternatingrather than constant to achieve optimum logging results. An alternatingmagnetic field minimizes electrode 129 polarization effects and alsominimizes effects of voltages induced by complex chemical and otherprocesses. Thus, an alternating electrical current may be applied to thecoils to obtain an alternating magnetic field 128.

[0082]FIG. 8A shows the measurement of water flow 113 with the sensorloop 108 in accordance with an embodiment of the present invention. Themagnetic field 128 is substantially perpendicular to water flow 113moving into, or out of, the wellbore 111 b. An induced signal voltage133 is generated and detected by a pair of electrodes 129 if aconductive fluid such as water is flowing substantially radially inwardor outward of the wellbore 111 b. The sensor loop 108 is sensitive onlyto water flowing radially. Radial inflow is distinguished from radialoutflow by the sign (e.g., +/−) of the signal voltage 133.Advantageously, the present sensor loop 108 is not sensitive to axialflow in the wellbore. Additionally, since the measurement principlerequires some small amount of fluid conductivity as virtually all waterhas, oil and gas flows will not be detected as they are insulators anddo not have the required minimum amount of conductivity. Thus the sensorloop 108 is sensitive only to the flow of conductive fluids such aswater, and only to lateral conductive fluid that is entering or leavingthe wellbore 111 b. In contrast, prior art techniques are also sensitiveto fluid movement inside the wellbore, and are sensitive tonon-conductive fluid movement such as oil and gas.

[0083]FIG. 9 shows a schematic of some electrical components within thesensor loop 108. The electrodes 129 are coupled to a resistor network.The electrodes 129 are coupled together with high resistance valueresistors 132 such that measured voltage, measured by voltage measuringdevice 110, is proportional to the fluid flow 113 velocity, if the flowis passed over or between at least one pair of electrodes 129. Resistors132 preferably range from 500,000 to 2,500,000 ohms and more preferablycomprise 1,000,000 or 2,000,000 ohm resistors, as examples. The flowrate 113 is proportional to the measured voltage 133.

[0084]FIG. 10A illustrates a top view of the sensor loop 108, includinga sensor loop body 136 which contains or is coupled to the sensor loop108 elements described previously herein. FIG. 10B shows an example of across-sectional view of the sensor loop 108.

[0085] If the orientation of the inflow or outflow is desired, as wouldbe useful in various applications, an alternative wiring and datasampling of the sensor loop 108 may be implemented, whereby eachelectrode 129 pair by itself is measured along with the azimuthal angleof the high side of the tool measurement. Thus, the orientation of theinflow or outflow may be determined.

[0086]FIG. 11 shows an example log 150 indicating the response of thepresent logging device described herein. On the log, the x-axisrepresents depth in feet, and the y-axis represents water flow rate inbarrels of water per day. When preferred embodiments of the presentinvention are lowered into this wellbore over the interval 7000 to 7100feet, a water inflow into the wellbore is detected at 7060 feet, shownat 152, in this example. No water inflow is detected except at 7060feet, as evident from the logging graph 150.

[0087] While preferred embodiments of the invention are described withreference to oil and gas wells and water-injection wells, preferredembodiments of the present logging device are also useful in detectingleaks in water pipelines and other fluid pipelines, for example. Otheralternative elements and features may be utilized with the presentlogging device. For example, an electromagnetic flow measurement in someother mode may be implemented, such as one pair of electrodes on arotating arm to sweep around the casing inner wall. A differentarrangement may be used to hold the sensor loop against the boreholewall, such as a telescoping loop, where the loop is perpendicular to thecasing axis, adapted to flip down into place after going below thetubing. Another means of holding the sensor loop again the borehole wallmay include a three or four point hold against the casing inner wallinstead of the two point hold disclosed. Rather than making the waterflow measurement directly against the borehole wall, the measurement maybe made a predetermined distance away from the casing inner wall, e.g.,⅛″ to ¾″. The logging device design may be simplified to accommodateonly one casing diameter, resulting in a simpler tool design. Ratherthan comprising a sensor loop as described herein, the radial sensingdevice 108 may alternatively comprise a plurality of small individualelectromagnetic sensors (e.g. one electrode pair) used on each of amultiply-armed caliper tool, although the sensors may not cover the fullborehole wall circumference in some cases. The preferred embodiments ofthe present invention are described herein for the measurement of thelateral inflow and outflow of water, however, preferred embodiments ofthe invention may also be utilized to measure the lateral flow of otherconductive fluids. The various example dimensions described herein mayvary according to a variety of factors such as how large the boreholeis, and the inner diameter dimensions of the casings and tubing withinthe borehole.

[0088] The novel logging device embodiments disclosed herein achievetechnical advantages by providing a logging device that is sensitiveonly to a conductive fluid such as water, and that is not sensitive tononconductive fluids such as oil or gas. Only water entering or leavingthe wellbore is sensed as it enters or leaves, and the sensor loop isnot sensitive to water already in borehole, whether the water is movingor not. The device is not sensitive to the complex flow regimes in thecenter of the wellbore, because the device measures the flow as itenters the wellbore along the wall and before it enters into the complexflow regimes in the wellbore center. The device is not required to inferthe cause of changes in above and below readings. The novel loggingdevice directly senses water entering or leaving the wellbore. Thedevice is not required to infer the type of fluid entered the borehole,as preferred embodiments of the invention are sensitive only to water.The measurement sensor loop has no moving sensor parts, as in some priorart logging instruments that comprise spinners, for example. The sensorloop has no threshold fluid velocity below which the measurementregisters no flow, thus it will sense even a small flow.

[0089] While most prior art logging devices must be passed through thewellbore more than once, e.g., typically six sets of readings to obtainan accurate reading, preferred embodiments of the present invention mayprovide an accurate reading in only one pass, e.g., one set of readings.For example, the logging device 140 need only be inserted once into theborehole, and then removed, resulting in each portion of the boreholebeing measured for conductive fluid flow as little as once and beingtraversed only twice. Additionally, varying diameters of borehole may beaccommodated with preferred embodiments of the present invention, withthe use of the side arms that automatically adjust the angle of thesensor loop with respect to the borehole central axis.

[0090] While preferred embodiments of the invention have been describedwith reference to illustrative embodiments, this description is notintended to be construed in a limiting sense. Various modifications incombinations of the illustrative embodiments, as well as otherembodiments of the invention, will be apparent to persons skilled in theart upon reference to the description. In addition, the order of processsteps may be rearranged by one of ordinary skill in the art, yet stillbe within the scope of preferred embodiments of the present invention.It is therefore intended that the appended claims encompass any suchmodifications or embodiments. Moreover, the scope of the presentapplication is not intended to be limited to the particular embodimentsof the process, machine, manufacture, composition of matter, means,methods and steps described in the specification. Accordingly, theappended claims are intended to include within their scope suchprocesses, machines, manufacture, compositions of matter, means,methods, or steps.

What is claimed is:
 1. A logging tool for a borehole, the boreholehaving an interior wall, the tool comprising: a tool body adapted to beinserted into the borehole; and a radial sensing device coupled to thetool body, the radial sensing device adapted to measure the flowvelocity of conductive fluid entering or leaving the borehole interiorwall, the radial sensing device being adapted to make the conductivefluid flow velocity measurements proximate the borehole wall.
 2. Thelogging tool according to claim 1, wherein the radial sensing devicecomprises a spring-loaded sensor loop, the sensor loop being adapted toexert outward pressure to maintain contact of the sensor loopsubstantially flush with the borehole interior wall while the tooltraverses the borehole.
 3. The logging tool according to claim 2,wherein the sensor loop includes a spring disposed within the sensorloop.
 4. The logging tool according to claim 3, wherein the sensor loopis adapted to be positioned at a non-perpendicular angle with respect tothe borehole central axis.
 5. The logging tool according to claim 4,wherein the sensor loop angle is between 10 to 80 degrees with respectto the borehole central axis.
 6. The logging tool according to claim 2,wherein the sensor loop is a continuous ring, wherein the inflow oroutflow of conductive fluid is detectable along the circumference of thesensor loop.
 7. The logging tool according to claim 6, wherein thesensor loop includes a plurality of sensors adapted to sense the flow ofconductive fluid over the sensor loop.
 8. The logging tool according toclaim 6 wherein the sensor loop comprises: a first coil of wire adaptedto generate a magnetic field just outside the sensor loop; a second coilof wire adapted to generate a magnetic field just outside the sensorloop; a ferromagnetic material disposed between the two coils; aplurality of resistors disposed along the sensor loop; a plurality ofelectrodes, each one of the electrodes coupled between two adjacentresistors along the loop circumference; and a voltage measuringmechanism electrically coupled between two of the resistors.
 9. Thelogging tool according to claim 2 wherein the sensor loop is adapted tooperate within a plurality of different diameter casings within a singlewell.
 10. The logging tool according to claim 9, wherein the sensor loopis coupled to the tool body at a loop high point and a loop low point,the loop high point and loop low point being about 180 degrees apartalong the sensor loop.
 11. The logging tool according to claim 10,further comprising: a first side arm coupled to the loop high point, thefirst side arm being flush to the borehole wall; and a second side armcoupled to the loop low point, the second side arm being flush to theborehole wall and being 180 degrees apart from the first side arm, thefirst and second side arms adapted to hold the upper and lower end ofthe sensor loop, respectively, against the borehole inner wall.
 12. Thelogging tool according to claim 11, wherein the tool body is positionedin a plane, wherein the first and second side arms are positioned in thetool body plane.
 13. The logging tool according to claim 11, furthercomprising: a force arm coupled between each end of the first and secondside arms and the tool body, wherein the force arms, side arms and toolbody lie in a common plane.
 14. The logging tool according to claim 13wherein the force arms at one end of the tool are axially fixed to thetool body, and the force arms at the other end of the tool are axiallymovable along the tool body.
 15. The logging tool according to claim 14wherein the tool body includes a slit, wherein the moveable force armsare coupled to the tool body via the slit to enable the tool toaccommodate different diameter casings.
 16. The logging tool accordingto claim 11 wherein the side arms include a sloped recessed interval toaccommodate the width of the sensor loop.
 17. The logging tool accordingto claim 1, wherein the radial sensing device is insensitive to the flowof nonconductive fluid.
 18. The logging tool according to claim 1,wherein the conductive fluid is water, wherein the radial sensing deviceis insensitive to the flow of water inside a central region of theborehole.
 19. A fluid flow measuring device, comprising: a plurality ofresistors disposed in a circular pattern; a plurality of electrodes,each electrode coupled between two adjacent resistors; a first coil ofwire adapted to generate a magnetic field wound proximate the resistorsand electrodes; a second coil of wire adapted to generate a magneticfield wound proximate the resistors and electrodes; and a voltagemeasuring mechanism electrically coupled between two of the resistors,wherein a flow of conductive fluid is detectable by measuring thevoltage.
 20. The fluid flow measuring device according to claim 19,further comprising a ferromagnetic material disposed between the twocoils.
 21. The fluid flow measuring device according to claim 19,wherein at least the resistors and electrodes are mounted on a sensorloop, the sensor loop being spring-loaded and being adapted to exertoutward pressure to maintain contact of the sensor loop substantiallyflush with a borehole interior wall.
 22. The fluid flow measuring deviceaccording to claim 19, further comprising: means for maintaining flushcontact of the sensor loop with a borehole interior wall over a range ofborehole casing diameters.
 23. A method of measuring lateral fluid flowin a borehole, comprising: traversing the borehole with a tool bodyhaving a sensor loop attached thereto, wherein the sensor loop isadapted to directly measure the flow velocity of conductive fluidentering or leaving the borehole interior wall.
 24. The method accordingto claim 23, further comprising the sensor loop maintaining in flushcontact with the interior wall of the borehole.
 25. The method accordingto claim 24, further comprising the sensor loop adjusting to a range ofdiameters of casings within the borehole.
 26. The method according toclaim 25, further comprising the sensor loop adapting to the boreholediameter range by changing the angle of the sensor loop with respect tothe central axis of the borehole.
 27. The method according to claim 23wherein each portion of the borehole being measured for conductive fluidflow is traversed only twice.
 28. The method according to claim 23wherein the conductive fluid comprises water.
 29. The method accordingto claim 23, wherein directly measuring the flow velocity comprises:generating a magnetic field proximate the sensor loop; and measuring thevoltage between electrodes positioned at intervals along the sensorloop.